1. Field of the Invention
The invention relates to RFID (Radio Frequency Identification) systems and, more particularly, to an RFID system designed to continuously track articles and personnel.
2. Background of the Invention
RFID systems are broadly divided into two categories: active and passive. Passive RFID systems operate without a battery, and may draw their power from a field emitted by interrogation devices or xe2x80x9creaders.xe2x80x9d Power is available only if the reader is close to the tags, for example, less than 2 meters. Therefore, passive systems can only be read at a limited number of fixed locations. Generally, passive readers include a powering element and a reading element in the same integrated unit.
Active RFID tags incorporate a battery, and therefore are capable of operating at much longer distances. In some premium products the xe2x80x9ctagsxe2x80x9d are full super-heterodyne radios. More typically, active tags operate at ranges up to about 5 meters. Other RFID technologies are designed to work at longer ranges, such as 30-100 meters. The intent is generally to enable the tag to be seen anywhere in an indoor facility, and an infrastructure is installed to provide total indoor coverage.
Thus, there is required a technique and system for combining active and passive tags into a single architecture, allowing very inexpensive passive tags to be used where high volume or unlimited life is required, and more expensive active tags to be used for lower volume applications where continuous tracking is required. By leveraging the long-range infrastructure, the passive subsystem can enjoy various cost, coverage, and performance improvements over a stand-alone passive RFID system.
In accordance with one aspect of the invention is a system and method for locating an object. A cell controller transmits a first signal at a first frequency. A first tag associated with the object receives the first signal and transponds the first signal at selected times at a second frequency as a second signal. The first tag is one of a passive tag or an active tag in which the passive tag has power from an external power source to transpond the second signal. The active tag has power from an internal power source to transpond said second signal. The cell controller includes a receiver for receiving said second signal.
Thus, there is provided a technique and system for combining active and passive tags into a single architecture, allowing very inexpensive passive tags to be used where high volume or unlimited life is required, and more expensive active tags to be used for lower volume applications where continuous tracking is required.